Microfluidics concerns the handling of in particular liquids within a very small space. Microfluidic systems are components which are used to move, control and analyze liquids on length scales of below 1 mm. By way of example, microfluidic systems are utilized for applications and measurements in modern biology, biotechnology, biochemistry, the pharmaceutical industry, analytic and clinical chemistry, environmental analysis or in process control.
Microfluidic systems in the form of test elements are often used for analyzing bodily fluids such as blood or urine. The samples to be analyzed are placed on a test element and there they may react with one or more reagents before they are analyzed. The optical, in particular the photometric, and the electrochemical evaluations of test elements constitute common methods for quickly determining the concentration of analytes in the sample. There are different types of test elements, for example there are capillary gap test elements, in which the sample liquid is moved in a transport channel (capillary channel, capillary gap) from a sample application location to a sample detection location, at a distance from said sample application location, using capillary forces in order to undergo a detection reaction at said sample detection location. Capillary gap test elements are disclosed in, for example, CA 2549143 or US 2003/0013147 A1. The typical capillary gap test elements comprise micro-capillaries that have an inner coating of hydrophilic and possibly also of hydrophobic materials. The liquid transport in microfluidic systems can be controlled by hydrophilic and hydrophobic surface properties of the materials contacting the sample liquid. In the prior art, polymer surfaces are functionalized (hydrophobized or hydrophilized), inter alia, by coating, for example from the gas-like, vapor-like, liquid, pulpy, or paste-like state, for example by spraying a suspension, from the ionized state by electrolytic or chemical deposition or from the solid state (i.e. granular or powdered state), for example by powder coating or coating by sintering. Moreover, it is for example known to build test elements from a plurality of foils having different wettabilities and lying on top of one another.
The structuring of a polymer layer by plasma etching or photoablation is also known in the art. Such methods typically have an ablating effect which generate a three-dimensional structure in interconnected polymer layers. The wettability of the structure surface changes depending on which of the polymer layers equipped with various surface properties is adjacent to a structure generated in this fashion. See, for example, WO 01/56771 A2.
It is also known to generate a surface pattern by means of photoablation. By way of example, a biological affinity reagent is applied in the photoablated region. See, for example, WO 98/23957 A1.
The methods for functionalizing the surface disclosed in the prior art can be subdivided into large-scale and spatially-resolved methods. Large-scale methods are disadvantageous in that they may complicate or impede further processing. By way of example, adhesively bonding a layer having certain surface properties results in troublesome adhesive remains. Alternate patterns of hydrophilic and hydrophobic functions (patterning) cannot be produced by large-scale methods. Spatially-resolved methods disclosed in the prior art are complicated and expensive. Producing small dimensions, i.e. a high resolution, is difficult. These spatially-resolved methods can in part only be applied on flat surfaces. There is little flexibility for changing the geometry.
It is the object of the invention to avoid the disadvantages of the prior art. In particular, it is an object of the invention to provide a method for producing a microfluidic system on a polymer surface in which the wettability of at least one portion of the polymer surface is modified in a cost-effective and flexible fashion.